Something else that might be worth a try:
"Mr. Sticky's underwater glue"

http://www.a-a-i.net/underwater.htm

-Wes

Don Hanson wrote:
> I posted earlier (from the Digest) asking if anyone knew what would mend a
> polyethylene water tank like we have from Westphalia.  Well, it seems that
> stuff is pretty 'slick' and not much sticks to it or bonds it.
> Traditionally, the only way to fix it has been to "weld" it somehow, using
> various welding systems.  I found this out from an involved search for info
> on the net.
>   But recently, 3M discovered an adhesive that actually works, and now
> markets it as 3M- product number 4693 and 4693h for a thicker version. But
> they only package it large.
>   Then I found on Tap Plastics page, and 'confirmed' by some chat list, a
> product using 3M's formula.  Heres the link to that product on Tap Plastic's
> page..BTW, Tap Plastics has all kinds of neat stuff..
> http://www.tapplastics.com/shop/product.php?pid=435&
>
>   So I am going to try some of this goo on my leaking tank..
>   Don Hanson
>
>